The present invention relates to an optical recording/reproducing apparatus comprising an optical head for applying a laser beam to an optical recording medium, thereby to record data on and reproduce data from the optical recording medium. More particularly, the present invention relates to an optical recording/reproducing apparatus for use in combination with a plurality of optical recording media, each having recording tracks formed at a track pitch different from the track pitch of any one of the other optical recording media, or with an optical recording medium that have a plurality of recording regions, each having recording tracks formed at a track pitch different from the track pitch of any one of the other recording regions.
Data recording media, such as playback-only optical discs, phase-change optical discs, magneto-optical discs and optical cards, are widely used to store video data, audio data and other data such as computer programs. In recent years it has been increasingly demanded that these data recording media should record data at higher densities and in greater amounts.
In recent years, compact discs (CDs), recordable compact discs (CD-Rs) and rewritable compact discs (CD-RWs) have come into use as means for recording data in computers. Hence, CD-R/RW apparatuses for recording data signals on, and reproducing them from, these optical recording media are used in increasing numbers.
It is increasingly required that a great amount of data, such as image data, be stored. It is therefore desirable to increase the recording capacity of optical recording media such as CD-Rs and CD-RWs.
As is known in the art, tracking error signals are generated by DPP (Differential Push Pull) method or three-spot method in the optical disc recording/reproducing apparatus for use in combination with optical discs such as CD-Rs and CD-RWs.
FIG. 1 shows the positional relation between beam spots on a disc and beam spots on a photodetector, illustrating how a tracking error signal is generated in the DPP method.
A main spot SPm of the main beam is formed on an optical disc 211, while side spots SPs1 and SPs2 of two side beams are formed the optical disc 211, too. The side spots SPs1 and SPs2 are spaced from the main spot SPm in the opposite radial directions, respectively, by a distance of Tp/2 (180xc2x0), where Tp is the intervals (track pitch) at which grooves GR (i.e., recording tracks) are arranged.
Photodiode sections 212M, 212S1 and 212S2 constitute a photodetector 212. Spots SPmxe2x80x2, SPs1xe2x80x2 and SPs2xe2x80x2 of light beams reflected from the optical disc 211, at the spots SPm, SPs1 and SPs2, are formed on the photodiodes 212M, 212S1 and 212S2, respectively. The photodiode section 212M comprises four photodiodes Da to Dd, which generate detection signals Sa to Sd. The photodiode section 212S1 comprises two photodiodes De and Df, which output detection signals Se and Sf. The photodiode section 212S2 comprises two photodiodes Dg and Dh, which output detection signals Sg and Sh.
FIG. 2 shows a circuit connection for generating a tracking error signal STE in the DPP method. A subtracter 221M subtracts the sum of the detection signals Sb and Sc from the sum of the detection signals Sa and Sd, generating a push-pull signal Sppm that corresponds to the light reflected from the main spot SPm. A subtracter 221S1 subtracts the detection signal Sf from the detection signal Se, generating a push-pull signal Spps1 that corresponds to the light reflected from the side spot SPs1. A subtracter 221S2 subtracts the detection signal Sh from the detection signal Sg, generating a push-pull signal Spps2 that corresponds to the light reflected from the side spot SPs2.
An adder 222 receives the push-pull signal Spps2 supplied via an amplitude adjuster 223 having gain G2. The adder 222 receives the push-pull signal Spps1, too. The adder 222 adds the push-pull signals Spps1 and Spps2, generating a sum signal Ss. A subtracter 224 receives the sum signal Ss via a amplitude adjuster 225 having gain G1. The substracter 224 receives the push-pull signal Sppm. The substracter 224 subtracts the sum signal Ss from the push-pull signal Sppm, generating a tracking error signal STE. Here, G1=A1/2A2, and G2=A2/A3, where A1 is the amplitude of the push-pull signal Sppm, A2 is the amplitude of the push-pull signal Spps1, and A3 is the amplitude of the push-pull signal Spps2. Thus, an offset is removed from the tracking error signal STE.
FIG. 3 depicts the positional relation between beam spots on a disc and beam spots on a photodetector, illustrating how a tracking error signal is generated in the three-spot method.
A main spot SPm of the main beam is formed on an optical disc 211, while side spots SPs1 and SPs2 of two side beams are formed the optical disc 211, too. The side spots SPs1 and SPs2 are spaced from the main spot SPm in the opposite radial directions, respectively, by a distance of Tp/4 (90xc2x0), where Tp is the intervals (track pitch) at which grooves GR (i.e., recording tracks) are arranged.
Photodiode sections 213M, 213S1 and 213S2 constitute a photodetector 213. Spots SPmxe2x80x2, SPs1xe2x80x2 and SPs2xe2x80x2 of light beams reflected from the optical disc 211, at the spots SPm, SPs1 and SPs2, are formed on the photodiodes 213M, 213S1 and 213S2, respectively. The photodiode section 213M comprises four photodiodes Da to Dd, which generate detection signals Sa to Sd. The photodiode section 213S1 comprises a photodiodes Df, which outputs a detection signalsSf. The photodiode section 213S2 comprises a photodiode De, which outputs a detection signals Se.
FIG. 4 illustrates a circuit connection for generating a tracking error signal STE in the three-spot method. A subtracter 226 subtracts the detection signal Sf from the detection signal Se, generating the tracking error signal STE.
To increase the recording capacity of such an optical recording medium as described above, it is advisable to enhance the linear density or the track density. If the linear density of the optical recording medium is increased, the jitter in the signal reproduced from the medium will increase due to inter-code interference, unless the optical system for recording data signals on and reproducing them from the medium is modified in specification. If the track density is increased without modifying the optical system, a crosstalk will develop to make it difficult to reproduce the data signals reliably.
The problems described above can be solved by modifying the optical system, thereby reducing the diameter of the reading beam spot.
To reduce the diameter of the beam spot, various methods may be used. One method is to decrease the wavelength of the laser beam applied in the optical system. Another method is to increase the numerical aperture (NA) of the objective lens incorporated in the optical system. If the wavelength of the laser beam is changed, however, data signals will be neither recorded on, nor reproduced from, the existing CD-R. This is because the dye film, or recording layer, of the CD-R has reflectance that greatly depends on the wavelength of the laser beam. Further, if the NA of the objective lens is excessively large, coma-aberration will occur as the disc warps with respect to the axis of the laser beam or spherical aberration will develop due to the uneven thickness of the disc. The aberration, whether coma-aberration or spherical aberration, will increase the jitter in the signal reproduced from the medium.
Consider the detection of tracking error signals in the process of recording data signals on, or reproducing them from, various kinds of discs, each having recording tracks formed at a track density (track pitch) different from the track density of any one of the other discs. Then, the following problems seem to arise. To generate a tracking error signal STE in the DPP method, the side spots SPs1 and SPs2 are spaced, as described above, from the main spot SPm in the opposite radial directions, respectively, by a distance of Tp/2(180xc2x0), where Tp is the intervals (track pitch) at which grooves GR (i.e., recording tracks) are arranged. Hence, the side spots SPs1 and SPs2 are spaced from the main spot SPm by 1.6/2 xcexcm (180xc2x0) in the opposite directions, as shown in FIG. 5A, in an optical disc drive that uses a CD (Compact Disc) having track pitch Tp of 1.6 xcexcm.
In such an optical disc drive which holds an optical disc 211S having the track pitch Tp of 1.6 xcexcm, the push-pull signals Sppm, Spps1 and Spps2 change as shown in FIGS. 5B, 5C and 5D, respectively, with the position the main spot SPm takes in the radial direction. In this case, the push-pull signals Spps1 and Spps2 are in the same phase. The tracking error signal STE therefore has a sufficient amplitude as is illustrated in FIG. 5E.
Assume that the optical disc drive holds an optical disc 211D which has a track pitch Tp of 1.07 xcexcm, i.e., two-thirds of the track pitch of CDs, and which therefore has greater recording capacity than CDs. If so, it will be difficult for the disc drive to generate tracking error signals STE that have a sufficient amplitude.
In this case, the side spots SPs1 and SPs2 are spaced from the main spot SPm by 1.6/2 xcexcm (270xc2x0) in the opposite directions, as shown in FIG. 6A, in an optical disc drive. Hence, the push-pull signals Sppm, Spps1 and Spps2 change as shown in FIGS. 6B, 6C and 6D, respectively, with the position the main spot SPm takes in the radial direction. The push-pull signals Spps1 and Spps2 are therefore in the opposite phases. The tracking error signal STE has but a small amplitude as is illustrated in FIG. 6E.
As indicated above, in an optical disc drive wherein the side spots SPs1 and SPs2 are spaced from the main spot SPm by 1.6/2 xcexcm in the opposite directions, the tracking error signal STE generated by the DPP method has an extremely small amplitude if the disc drive holds an optical disc 211D which has a track pitch Tp of 1.07 xcexcm, i.e., two-thirds of the track pitch of CDs. It is therefore difficult to use the optical disc 211D having track pitch Tp of 1.07 xcexcm in this optical disc drive.
As mentioned above, too, the side spots SPs1 and SPs2 are spaced from the main spot SPm in the opposite radial directions, respectively, by a distance of Tp/4 in the process of generating a tracking error signal STE by means of the three-spot method. Thus, in an optical disc drive that holds a disc having a track pitch Tp of 1.6 xcexcm as CDs, the side spots SPs1 and SPs2 are spaced from the main spot SPm in the opposite radial directions, respectively, by a distance of 1.6/4 xcexcm (90xc2x0) as is illustrated in FIG. 7A.
Assume that this optical disc drive holds an optical disc 211S which has a track pitch Tp of 1.6 xcexcm. Then, the main signal Sm (i.e., the sum of detection signals Sa and Sd), the detection signal Se and detection signal Sf change as shown in FIGS. 7B, 7C and 7D, respectively, with the position the main spot SPm takes in the radial direction. The detection signals signals Se and Sf are therefore in the opposite phases. The tracking error signal STE has a sufficient amplitude as is illustrated in FIG. 7E.
Let us assume that this optical disc drive holds an optical disc 211D which has a track pitch Tp of 1.07 xcexcm, i.e., two-thirds of the track pitch of CDs and which therefore has greater recording capacity than CDs. It is therefore difficult for the disc drive to generate tracking error signals STE that have a sufficient amplitude.
In this case, the side spots SPs1 and SPs2 are spaced from the main spot SPm by 1.6/4 xcexcm (135xc2x0) in the opposite directions, as shown in FIG. 8A, in an optical disc drive. The main signal Sm, detection signal Se and detection signal Sf therefore change as shown in FIGS. 8B, 8C and 8D, respectively, with the position the main spot SPm takes in the radial direction. The push-pull signals Spps1 and Spps2 are therefore in the opposite phases. The detection signals Se and Sf are not in the opposite phases. It follows that the tracking error signal STE has but a small amplitude as is illustrated in FIG. 8E.
As indicated above, in an optical disc drive wherein the side spots SPs1 and SPs2 are spaced from the main spot SPm by 1.6/4 xcexcm in the opposite directions, the tracking error signal STE generated by the three-spot method has an extremely small amplitude if the disc drive holds an optical disc 211D which has a track pitch Tp of 1.07 xcexcm, i.e., two-thirds of the track pitch of CDs. Thus, it is difficult to use the optical disc 211D having track pitch Tp of 1.07 xcexcm in this optical disc drive.
This invention has been made in consideration of the foregoing. The first object of the invention is to provide an optical recording/reproducing apparatus that can reliably record and reproduce data on and from not only the existing optical recording media, but also a high-density recording medium.
The second object of the invention is to provide an optical recording/reproducing apparatus that can generates a tracking error signal which is a desirable one, regardless of the track pitch of the recording medium used in the apparatus.
An optical recording/reproducing apparatus according to the invention is designed for use in combination with recording media that differ in track pitch, or a recording medium having recording regions that differ in track pitch. The apparatus comprises: drive means for rotating a recording medium; an optical head for applying light to the recording medium being rotated by the drive means, thereby to record data signals on the recording medium or reproducing data from the recording medium; and a signal-processing circuit for processing a signal detected by the optical head. The optical head comprises a light source for emitting light, an objective lens for condensing the light emitted by the light source on the recording medium and signal-detecting means for receiving the light reflected from the recording medium, thereby to detect signals. The objective lens has a numerical aperture NA, where 0.5 less than NAxe2x89xa60.6.
The objective lens has a numerical aperture NA, where 0.5 less than NAxe2x89xa60.6 in the optical recording/reproducing apparatus. The apparatus can, therefore, reliably record data on and reproduce data from a high-density optical recording media that have different track pitches.
An optical disc drive according to the invention is designed for use in combination with optical discs, each having recording tracks and differing in track pitch from any other optical disc, or an optical disc having recording regions, each having recording tracks and differing in track pitch from any other recording region. The optical head drive comprises: light beam applying means for forming a main spot, a first side spot and a second side spot on the optical disc, said first and second spots spaced apart from the main spot in the opposite radial directions; error signal generating means for generating a tracking error signal from light reflected from at least the first and second side spots, said tracking error signal representing a distance by which the main spot deviates from any recording track in the radial direction; and tracking control means for controlling the light beam applying means in accordance with the tracking error signal, thereby to move the main spot to a predetermined position on the recording track. The light beam applying means forms the first and second side spots, each between a first position and a second position. The first position is one each side spot takes to generate a tracking error signal of a maximum amplitude when the optical disc is one that has the longest track pitch. The second position is one each side spot takes to generate a tracking error signal of a maximum amplitude when the optical disc is one that has the shortest track pitch.
The first and second side spots are formed between the first position each side spot takes to generate a tracking error signal of a maximum amplitude when the optical disc and the second position each side spot takes to generate a tracking error signal of a maximum amplitude when the optical disc is one that has the shortest track pitch. Hence, the error signal generating means can generate a tracking error signal that has sufficient amplitude, regardless of the tracking pitch of the optical disc held in the disc drive. Thus, the disc drive can record and reproduce data on and from optical discs, each having recording tracks and differing in track pitch from any other optical disc, or an optical disc having recording regions, each having recording tracks and differing in track pitch from any other recording region.
The amplitude of the tracking error signal generated from the light reflected from an optical disc depends on the tracking pitch of the optical disc. In view of this, the optical disc drive may further comprise gain control means for controlling the gain of the error signal generating means, thereby causing the error signal generating means to generate a tracking error signal that has the same amplitude for different track pitches.
As has been described, the present invention can provide an optical recording/reproducing apparatus that can reliably record and reproduce data on and from not only the existing optical recording media, but also a high-density recording medium, by using an optical pickup having a specified numerical aperture and by making the pits smaller.
Moreover, the invention can provide an optical recording/reproducing apparatus, wherein a main spot, a first side spot and a second side spot are formed on the optical disc. The first and second spots spaced apart from the main spot in the opposite radial directions. A tracking error signal is generated from light reflected from at least the first and second side spots. The tracking error signal represents a distance by which the main spot deviates from any recording track in the radial direction. In accordance with the tracking error signal, the main spot is moved to a predetermined position on the recording track. The first and second side spots are located, each between a first position and a second position. The first position is one each side spot takes to generate a tracking error signal of a maximum amplitude when the optical disc is one that has the longest track pitch. The second position is one each side spot takes to generate a tracking error signal of a maximum amplitude when the optical disc is one that has the shortest track pitch. Therefore, the apparatus can generate a tracking error signal of sufficient amplitude, regardless of the track pitch of the optical disc. Additionally, the apparatus can record and reproduce data on and from optical discs, each having recording tracks and differing in track pitch from any other optical disc, or an optical disc having recording regions, each having recording tracks and differing in track pitch from any other recording region.